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author | Petteri Aimonen <jpa@git.mail.kapsi.fi> | 2020-06-18 16:37:37 +0200 |
---|---|---|
committer | Borislav Petkov <bp@suse.de> | 2020-06-29 10:02:23 +0200 |
commit | 4185b3b92792eaec5869266e594338343421ffb0 (patch) | |
tree | ac708daf001002b2058ff899c74462500684e85c /lib | |
parent | 7ad816762f9bf89e940e618ea40c43138b479e10 (diff) | |
download | linux-4185b3b92792eaec5869266e594338343421ffb0.tar.bz2 |
selftests/fpu: Add an FPU selftest
Add a selftest for the usage of FPU code in kernel mode.
Currently only implemented for x86. In the future, kernel FPU testing
could be unified between the different architectures supporting it.
[ bp:
- Split out from a conglomerate patch, put comments over statements.
- run the test only on debugfs write.
- Add bare-minimum run_test_fpu.sh, run 1000 iterations on all CPUs
by default.
- Add conditionally -msse2 so that clang doesn't generate library
calls.
- Use cc-option to detect gcc 7.1 not supporting -mpreferred-stack-boundary=3 (amluto).
- Document stuff so that we don't forget.
- Fix:
ld: lib/test_fpu.o: in function `test_fpu_get':
>> test_fpu.c:(.text+0x16e): undefined reference to `__sanitizer_cov_trace_cmpd'
>> ld: test_fpu.c:(.text+0x1a7): undefined reference to `__sanitizer_cov_trace_cmpd'
ld: test_fpu.c:(.text+0x1e0): undefined reference to `__sanitizer_cov_trace_cmpd'
]
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Petteri Aimonen <jpa@git.mail.kapsi.fi>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/20200624114646.28953-3-bp@alien8.de
Diffstat (limited to 'lib')
-rw-r--r-- | lib/Kconfig.debug | 11 | ||||
-rw-r--r-- | lib/Makefile | 24 | ||||
-rw-r--r-- | lib/test_fpu.c | 89 |
3 files changed, 124 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 9ad9210d70a1..5842885ab184 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2307,6 +2307,17 @@ config TEST_HMM If unsure, say N. +config TEST_FPU + tristate "Test floating point operations in kernel space" + depends on X86 && !KCOV_INSTRUMENT_ALL + help + Enable this option to add /sys/kernel/debug/selftest_helpers/test_fpu + which will trigger a sequence of floating point operations. This is used + for self-testing floating point control register setting in + kernel_fpu_begin(). + + If unsure, say N. + endif # RUNTIME_TESTING_MENU config MEMTEST diff --git a/lib/Makefile b/lib/Makefile index b1c42c10073b..d0f17a74afaf 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -99,6 +99,30 @@ obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o obj-$(CONFIG_TEST_HMM) += test_hmm.o +# +# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns +# off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS +# get appended last to CFLAGS and thus override those previous compiler options. +# +FPU_CFLAGS := -mhard-float -msse -msse2 +ifdef CONFIG_CC_IS_GCC +# Stack alignment mismatch, proceed with caution. +# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 +# (8B stack alignment). +# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383 +# +# The "-msse" in the first argument is there so that the +# -mpreferred-stack-boundary=3 build error: +# +# -mpreferred-stack-boundary=3 is not between 4 and 12 +# +# can be triggered. Otherwise gcc doesn't complain. +FPU_CFLAGS += $(call cc-option,-msse -mpreferred-stack-boundary=3,-mpreferred-stack-boundary=4) +endif + +obj-$(CONFIG_TEST_FPU) += test_fpu.o +CFLAGS_test_fpu.o += $(FPU_CFLAGS) + obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/ obj-$(CONFIG_KUNIT) += kunit/ diff --git a/lib/test_fpu.c b/lib/test_fpu.c new file mode 100644 index 000000000000..c33764aa3eb8 --- /dev/null +++ b/lib/test_fpu.c @@ -0,0 +1,89 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * Test cases for using floating point operations inside a kernel module. + * + * This tests kernel_fpu_begin() and kernel_fpu_end() functions, especially + * when userland has modified the floating point control registers. The kernel + * state might depend on the state set by the userland thread that was active + * before a syscall. + * + * To facilitate the test, this module registers file + * /sys/kernel/debug/selftest_helpers/test_fpu, which when read causes a + * sequence of floating point operations. If the operations fail, either the + * read returns error status or the kernel crashes. + * If the operations succeed, the read returns "1\n". + */ + +#include <linux/module.h> +#include <linux/kernel.h> +#include <linux/debugfs.h> +#include <asm/fpu/api.h> + +static int test_fpu(void) +{ + /* + * This sequence of operations tests that rounding mode is + * to nearest and that denormal numbers are supported. + * Volatile variables are used to avoid compiler optimizing + * the calculations away. + */ + volatile double a, b, c, d, e, f, g; + + a = 4.0; + b = 1e-15; + c = 1e-310; + + /* Sets precision flag */ + d = a + b; + + /* Result depends on rounding mode */ + e = a + b / 2; + + /* Denormal and very large values */ + f = b / c; + + /* Depends on denormal support */ + g = a + c * f; + + if (d > a && e > a && g > a) + return 0; + else + return -EINVAL; +} + +static int test_fpu_get(void *data, u64 *val) +{ + int status = -EINVAL; + + kernel_fpu_begin(); + status = test_fpu(); + kernel_fpu_end(); + + *val = 1; + return status; +} + +DEFINE_SIMPLE_ATTRIBUTE(test_fpu_fops, test_fpu_get, NULL, "%lld\n"); +static struct dentry *selftest_dir; + +static int __init test_fpu_init(void) +{ + selftest_dir = debugfs_create_dir("selftest_helpers", NULL); + if (!selftest_dir) + return -ENOMEM; + + debugfs_create_file("test_fpu", 0444, selftest_dir, NULL, + &test_fpu_fops); + + return 0; +} + +static void __exit test_fpu_exit(void) +{ + debugfs_remove(selftest_dir); +} + +module_init(test_fpu_init); +module_exit(test_fpu_exit); + +MODULE_LICENSE("GPL"); |